Almost 10 years ago James Howells threw away a hard drive during a clear out - forgetting about the Bitcoin on it.
Now, with the Bitcoin worth an estimated £150m ($184m), he is planning to spend millions digging up a Newport landfill in a bid to find the lost hard drive.
If recovered Mr Howells said he would give 10% of the proceeds to turn the city into a crypto-currency hub.
But the council said excavating the site would pose an ecological risk.
Mr Howells, an IT engineer, accidentally threw away the hard drive in 2013 after mining 8,000 Bitcoins in the early stages of the currency's development.